[PD] Add control to slow down a server (#5572)

python/sglang/srt/entrypoints/http_server.py

@@ -62,6 +62,7 @@ from sglang.srt.managers.io_struct import (
     ResumeMemoryOccupationReqInput,
     SeparateReasoningReqInput,
     SetInternalStateReq,
+    SlowDownReqInput,
     UpdateWeightFromDiskReqInput,
     UpdateWeightsFromDistributedReqInput,
     UpdateWeightsFromTensorReqInput,
@@ -494,6 +495,19 @@ async def resume_memory_occupation(
         return _create_error_response(e)
 
 
+@app.api_route("/slow_down", methods=["GET", "POST"])
+async def slow_down(obj: SlowDownReqInput, request: Request):
+    """Slow down the system deliberately. Only for testing. Example scenario:
+    when we want to test performance of D in large-scale PD disaggregation and have no enough nodes for P,
+    we can use this to slow down D to let it have enough running sequences, and then disable slowdown
+    to let it run in full batch size.
+    """
+    try:
+        await _global_state.tokenizer_manager.slow_down(obj, request)
+    except Exception as e:
+        return _create_error_response(e)
+
+
 @app.api_route("/open_session", methods=["GET", "POST"])
 async def open_session(obj: OpenSessionReqInput, request: Request):
     """Open a session, and return its unique session id."""